Key Points

• A lung ventilation/perfusion scan, or VQ scan, is a test that measures air and blood flow in your lungs.
• The test most often is used to help diagnose or rule out a pulmonary embolism (PE). The scan also can detect poor blood flow in the lungs’ blood vessels and provide pictures that help doctors prepare for some types of surgery.
• People who have signs or symptoms of a PE may need VQ scans. These signs and symptoms may include chest pain, trouble breathing, rapid breathing, coughing, coughing up blood, rapid heart rate, and pain or swelling in a leg.
• Most people don’t need to prepare for VQ scans. Your doctor may ask you to wear clothing that has no metal hooks or snaps. These materials can block the scanner’s view. Or, you may be asked to wear a hospital gown for the test.
• Tell your doctor whether you’re pregnant or may be pregnant. If possible, you should avoid unnecessary radiation exposure during pregnancy. This is because of the concern that radiation may harm the fetus.
• During the VQ scan, you will lie still on a table for about 1 hour and have two types of scans: ventilation and perfusion. A ventilation scan shows where air flows in your lungs. A perfusion scan shows where blood flows in your lungs. If you’re having trouble staying still, your doctor may give you medicine to help you relax.
• Both scans use radioisotopes (a low-risk radioactive substance). This substance releases energy inside your body. The scanner uses this energy to create images of air and blood flow in your lungs.
• Most people can return to their normal routines right after a VQ scan. If you got medicine to help you relax during the scan, your doctor will tell you when you can return to your normal routine. The medicine may make you tired, so you’ll need someone to drive you home.
• If you’re breast-feeding, ask your doctor how long you should wait after the test before you breast-feed. The radioisotopes used for VQ scans can be passed to your baby through your breast milk. You may want to prepare for the scan by pumping and saving milk for 24 to 48 hours in advance. You can bottle-feed your baby in the hours after the scan.
• Normal results from a VQ scan will show full air and blood flow to all parts of your lungs. If air flow is normal but blood flow isn’t, you may have a PE. However, a VQ scan alone can’t diagnose a PE. Your doctor will use the VQ scan results and the results from a physical exam, chest x ray, and other tests to make a diagnosis.
• VQ scans involve little pain or risk for most people. The radioisotopes used for both tests expose you to a small amount of radiation. Very rarely the radioisotopes can cause an allergic reaction. Hives or a rash may result. Medicines can relieve this reaction.